I've just recently taken in an old iMac my school systems used to use before they replenished them with newer Macs. I remember actually using this special model iMac in 2008, before they were removed. I found one, and took it in to use. My friend gave me a power cord for it, and I tried to see if it would run, to make sure it worked. but it didn't turn on at all. My friend said it probably was because the computer didn't recognize a keyboard/mouse in, and wouldn't boot.

Is this true?

Computers should turn on without a keyboard/mouse.. You just wouldn't be able to do anything without an input device

It would turn on without a keyboard and mouse, its probably a hardware issue.